Remove force push from GitCheckout.commit()

Remove force push from GitCheckout.commit()

The CQ should not be able to force push -- this allows it to wipe out legitimate
commits if something goes wrong internally. This happened recently, with a CQ
commit orphaning 20 commits from the previous few days. This may have happened
any number of times previously, probably only wiping out one commit at a time,
whenever there was a race between the CQ and a developer's direct commit+push.

Repositories should also protect themselves by disallowing force push in their
ACLs.

BUG=261619
Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=258092

[M-A Ruel, 2014-03-19 19:17:57]

lgtm

[Sergey Berezin, 2014-03-19 19:19:21]

lgtm

[rmistry, 2014-03-19 19:46:44]

On 2014/03/19 19:19:21, Sergey Berezin wrote:
> lgtm

LGTM

[iannucci, 2014-03-19 20:11:02]

On 2014/03/19 19:46:44, rmistry wrote:
> On 2014/03/19 19:19:21, Sergey Berezin wrote:
> > lgtm
> 
> LGTM

LGTM! Congratulations everyone on this momentus CL!

[agable, 2014-03-19 21:05:43]

The CQ bit was checked by agable@chromium.org

[commit-bot: I haz the power, 2014-03-19 21:05:52]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/agable@chromium.org/196573041/1

[commit-bot: I haz the power, 2014-03-19 21:07:40]

Change committed as 258092